Olive oil is definitely something where you can go quite a bit higher than the cheapest brands (even the cheapest "Extra virgin" olive oil) and really taste the difference. Say, up to £10/£20 for a 1/2 litre bottle. Possibly higher, but I've not tested more expensive brands than that. Cheaper olive does have some flavour, but is mainly a carrier for other foods and tastes. Really good olive oil tastes absolutely amazing just dipping bread (or even a finger) into it.

I certainly don't buy such olive oil regularly, but I can easily tell the difference if I do.